Machines exist for the fine machining of the tooth flanks of spur gears, in which a spur gear tool, which is made of an abrasive compound in a bonded matrix and which can have internal or external teeth, meshes with a spur gear workpiece. The removal on the flanks of the spur gear occurs by driving the tool or the workpiece and at the same time feeding radially. The spur gear tool is fitted or dressed beforehand with its own tool, e.g. a diamond coated dressing spur gear. Normally the axes of the tool and spur gear workpiece are not parallel, but rather crossed, so that even in the pitch circle the axial component still results in a relative movement and thus removal of material. With a dull or inaccurately shaped spur gear tool, the re-profiling is done by means of a radial infeed movement of the dressing spur gear.
The dressing operation changes the diameter of the spur gear tool, and in particular an externally toothed wheel becomes smaller and an internally toothed wheel becomes larger. This change in the diameter is equivalent to a profile displacement of the spur gear tool. Since, however, a profile displacement with undisturbed meshing of the teeth is geometrically possible only in a limited range which is dependent primarily on the number of teeth and the meshing angle, the spur gear tool can only be utilized in a narrow diameter range.
Another drawback of this fine machining process follows from the displacement of the point of contact on the spur gear workpiece as a consequence of the continuous, dressing-induced profile change or displacement of the spur gear tool. The relative speeds between the spur gear workpiece and tool thus change, as do the removal rate and in particular the tool marks on the tooth flank, rendering a constant finishing dubious or at least making it difficult.